Take a look at Lake Geneva. A very nice lake. A good lake to take your ski boat on. Big enough that you can stretch your legs with a 70mph boat, but anything more will be too big. I've heard that it now has a 45mph speed limit though. There are a couple of restaurants on the water too. If you really want to stretch your legs, then head up to Winnebago. The noise natzi's are nuts up there, but the lake is just huge.